Navigation of individuals requires knowledge of current position. Global Position System (GPS) satellite signals can be used to determine the current position, direction of motion, and speed (velocity) of a user via hand-held or vehicle-mounted GPS-equipped devices. At times, however, reception of the necessary GPS signals cannot be ensured, and alternate or supplemental systems and techniques are needed for determining an observer's current location and velocity for navigation control and other applications in which position and velocity information are useful.